1. Field of the Invention
The present invention relates to a polymerizing apparatus for polymerizing a monomer having an ethylenically unsaturated double bond wherein in a polymerization is carried out in a polymerization vessel while a reaction mixture is circulated through a heat exchanger installed separately from the polymerization vessel.
2. Description of the Prior Art
The polymerization reaction of a monomer having an ethylenically unsaturated double bond is carried out in such a manner that a polymerization medium such as water, a dispersant, a polymerization initiator, a monomer having an ethylenically unsaturated double bond, and, optionally, other various additives are charged into a polymerization vessel equipped with a jacket and a reflux condenser, then the temperature in the polymerization vessel is elevated and the polymerization reaction is effected while a certain temperature is kept. Further, during this polymerization reaction, in order to retain the inside of the reaction vessel at that certain temperature, it is required to remove the heat of polymerization reaction, so that cooling water is circulated through the jacket and the reflux condenser.
In recent years, in order to improve the productivity, the following measures are taken: (1) the polymerization vessel is made large in size and (2) the polymerization time per batch is shortened. However, since the enlargement of the polymerization vessel has resulted in a decrease in the ratio of the heat transfer area to the volume of the reaction mixture, the above prior technique of removing the heat of polymerization reaction has become insufficient in capacity for removing the heat. In addition, if the polymerization time per batch is shortened, the capacity for removing the heat becomes insufficient further because the rate of the generation of heat due to the polymerization reaction per unit time increases.
Some techniques for overcoming the above disadvantages are suggested and, as effective techniques out of them, techniques wherein a reaction mixture is circulated through a heat exchanger installed outside a polymerization vessel (see Japanese Pre-examination Patent Publication (kokai) Nos. 54-24991 (1979), 56-47410 (1981), and 58-32606 (1983) and Japanese Patent Publication (kokoku) No. 64-11642 (1989)) can be mentioned. These techniques are quite effective in that the ratio of the heat transfer area to the volume of the reaction mixture can be increased.
However, according to these techniques, there is a problem that polymer scale or a polymer in the form of blocks which is supposed to be formed in a circulating line made up of the heat exchanger and a circulating pipeline connecting the heat exchanger and the polymerization vessel blocks up the circulating pipeline or heat exchanger tubes. Further, when the obtained polymer is worked into a molded product such as a sheet, fish eyes increase.